2 19 



muscle is very shallow and the adductor ridge is very feebly indicated; the cavity for the 

 lateral depressor muscle is somewhat more distinct. 



The tergurn (PI. XXII, fig. 12, l> and d) is short and rather broad. lts scutal margin 

 is straight, its apex slightly, though not sharply pointed ; its carinal margin is very feebly 

 convex, and the two parts of the basal margin form together a straight line on opposite sides 

 of the spur. Externally the tergum shows rather distinct growth-ridges and an open longitu- 

 dinal furrow. The spur, which is obliquely truncated at the extremity, has a rather long free- 

 extencling part. Its width is about one fifth of the breadth of the entire valve. On the inner 

 surface the articular ridge is long, but not very prominent, and the articular furrow is not very 

 deep. The crests for the lateral depressor muscles are hardly visible. 



With regard to the structure of the animal's body the following seems of interest: 



Mouth. Labrum (PI. XXII, iïg. 13) with shallow notch, wide at entrance and three 

 teeth on each side of it; the sub-triangular portion is not very broad but rather elongate. 



The pal pi are elongately oval, with the extremity rounded. The outer surface is furnished 

 with a row of long and slender spine-like hairs standing at some distance from each other; 

 near the free extremity the same surface is furnished moreover with a group of not very 

 numerous hairs which pass imperceptably into the rather dense row of shorter hairs arranged 

 along the upper margin. The hairs on the inner surface are short and delicate and grouped 

 in the ordinary way : a longitudinal row is arranged in a line almost parallel to the upper 

 margin and these hairs are directed towards the free edge of the labrum. 



Mandible (PI. XXII, fig. 14). Distance of the extremities of teeth 1 and 2 greater 

 than that between 2 and 3, in the proportion as 4 to 3. Teeth 1 and 2 pointed, 3 thick 

 and indistinctly doublé. Tooth 4 is small, tooth 5 and inferior angle are represented by 

 small nobs. 



Maxi 11a (PI. XXII, fig. 15) with the edge straight, without a notch behind the upper 

 pair of larger spines, and with five somewhat shorter spines on the middle part of the edge 

 and two larger spines situated near the inferior angle, which itself bears a few shorter bristles. 

 Several delicate hairs are observable between the spines. 



Outer m a x i 1 1 a e have the outer lobe elongately oval, and over a large part (the 

 outer half) of the inner surface densely clothed with hairs, rather numerous ones being arranged in 

 a row over the inferior half of the same surface; the inner lobe has the interior face rounded 

 and furnished with not very numerous, but rather long and feathered hair-like spines. 



Cirri. First pair with the rami very unequal, of 6 to 7 and 16 segments. Inferior 

 segments with the inner faces somewhat protuberant. 



Second pair with short rami, of 5 and 6 segments; the inner faces rounded and not 

 protuberant, densely clothed with brushes of spine-like hairs. 



Third pair considerably longer than cirri of second pair, having respectively 8 and 9 

 segments in the two branches. Second to penultimate segments (PI. XXII, fig. 16) of both 

 rami having the rounded inner faces artned with numerous teeth, grouped in rows, and diminishing 

 in size from the front margin (where they appear like strong downwardly-curved teeth), over 

 the surface, to the posterior margin. 



9 1 



